[Kst] [Bug 117822] double click on a curve only works if you are near an actual data point

[Barth Netterfield]

The problem comes when we have a low density curve with long lines between 
points.  It is not always clear where the points are, and clicking on the 
line doesn't work; as you say, you have to click near the point.

This is a >=1.2.1 issue.

cbn